Total knee replacement technology is to be assessed for both its clinical and economic costs and benefits among rheumatoid arthritis and osteoarthritis patients at The Hospital for Special Surgery, Cornell Medical Center, New York City. We will assess clinical outcome of the surgery by comparing pre- and post-operative measures of medical status (physical examination, functional examination using the HSS Knee Rating Scale, gait analysis) and of psychological status (Adjective Check List and the Cattell Sixteen Personality Factor Questionnaire). The proposed economic cost-benefit analysis will be based on comparing economic expenditures and productivity (i.e., work and restricted activity) losses sustained in the year prior to and including total knee replacement surgery with those incurred in the year following surgery. The major source of economic data will be questionnaires administered to all patients. Validation (private physicians' records, clinic records, Medicare/Medicaid tapes) of patients' self-reported economic data will also be included in this study. In addition to the assessment, we intend to validate an instrument, the HSS Knee Rating Scale, designed to assess function following knee replacement, and to employ this and other measures in order to identify covariates of clinical outcome. It is anticipated that using such data one might be able to predict, in the future, which patients will benefit most from total knee replacement.